A common requirement in image editing or processing is to select a subset of pixels from an image, e.g. pixels that are of similar color. The selected pixels can then be processed together, e.g. to alter their color or to perform a copy command or a cut and paste command or the like.
Conventional approaches to color representation define a color in terms of co-ordinates in a color space. Known color encodings include for example RGB, SWOP, CYM(K), XYZ and CIELAB, with different encodings suited to different applications.
The RGB color model uses a rectangular co-ordinate system with an axis assigned to each of red, green and blue color components. These three components are termed ‘additive primaries’, as they are combined together to produce other colors. This model is used for example in CRT monitors and color raster graphics.
The CMY(K) color model is used primarily for printing and comprises cyan, magenta and yellow components, and often also uses a black component. These components are termed ‘subtractive primaries’ as one or more of these primaries are removed from white light to produce different colors.
In a typical process for selecting a sub-set of image pixels from a digital image, a user imports the image into an image processing program, and selects one of the pixels of the displayed image. The color attributes of the selected image pixel are determined, e.g. its RGB values, and all pixels in the image having the same RGB values to within a set tolerance are selected. The tolerance may be a number from 0 to 255 for RGB-coded images or from 0 to 100 for CYM(K)-coded images. The user can then act on the selected sub-set of pixels in whatever manner is desired.
These known selection processes however can be problematic, and it can be difficult for users to use these processes to accurately select the pixel sub-sets that they require. One problem for example is that a user may see little obvious relationship between a tolerance value and the pixel colors that the process will then select. Also, the pixel color ranges that are selectable are generally limited to regular geometric shapes within the color space.
The present invention aims to provide an alternative form of image element selection that, in its various embodiments, may have a number of advantages and may for example facilitate the automatic selection of pixels so as to conform well to a user's desired selection.